Hydraulic controls

ABSTRACT

A hydraulic circuit particularly useful for a loader vehicle is provided with a main pump and an auxiliary pump. The flow of the auxiliary pump may be selectively added to the flow of the main pump but is diverted to the reservoir if the system pressure rises above a predetermined level. A delay device is incorporated in the control to prevent rapid switches of the auxiliary pump into and out of the main circuit and so prevent undesirable vibrations in the loader vehicle.

' United States Patent 11 1 Machens et al. Nov. 4, 1975 HYDRAULIC CONTROLS 3,171,247 3/1965 McAlvay 60/486 x Inventors: KarLHeinz Machens Hannover; 3,443,380 5/1969 Karazl a 60/421 Erich Reupke, Wennigsen; Gerhard Isensee, Hannover, all of Germany Primary ExammerEdgar W. Geoghegan [73] Asslgnee: Massey'Ferguson servlces Attorney, Agent, or FirmThomas P. Lewandowski Curacao, Netherlands [22] Filed: Nov. 13, 1974 [21] Appl. N0.: 523,378

[57] ABSTRACT [30] Foreign Application Priority Data Nov. 14 1973 Germany 2356809 A hydraulic circuit Particularly useful for a loader hicle is provided with a main pump and an auxiliary 52 us. c1. 60/394; 60/428; 60/468; P The flew of the euxlhery m may he e e' 60/486. 60/1316. 2 tively added to the flow of the mam pump but 18 di- 51 lm. cl. i151; 11/16 verted to the reservoir if the system Pressure rises [58] Field of Search 60/394 421 428 430 above a predetermined level. A delay device is incor- 60/468 4 porated in the control to prevent rapid switches of the v auxiliary pump into and out of the main circuit and so [56] References Cited prevent undesirable vibrations in the loader vehicle.

UNITED STATES PATENTS 2,323,519 7/1943 Dean 60/DIG. 2 8 Claims, 5 Drawing Figures Sheet 1 of4 U.S. Patent Nov. 4, 1975 US. Patent Nov. 4, 1975 Sheet 2 of4 3,916,624

Sheet 3 of 4 U.S. Patent Nov. 4, 1975 nvnmuuc contracts The invention relates to hydraulic controls especially those used for heavy construction vehicles which are equipped with hydraulically operated ancillary implements such as buckets, blades or forks.

It is known from German Offenlegungschrifft No. 2,012,752 for such vehicles to be equipped with an engine-driven hydraulic pump for supplying an implement circuit and a standby pump the flow from which can be added or cut-in to the hydraulic system for the purpose of providing additional capacity for special circumstances of operation.

The cut-in of the standby pump ensures that for each operating condition there is a sufficient but not excessive machine capacity available to deal with it. When the pressure in, for instance, the implement circuit reaches a certain predetermined value the standby pump flow is cut-out and is returned directly to the tank. Certain drawbacks exist with the arrangement just described. Circumstances can arise where, for instance, on lifting a heavy load in a bucket, the predetermined pressure is reached and the standby pump flow is cut-out. Thereupon a pressure drop pulse occurs in the circuit causing the pressure to fall below the predetermined value thus causing the standby pump flow to be cutin again. The increased flow causes a pressure increase pulse which signals for the standby pump flow to be cut-out. This repeated sequence occurs very rapidly causing vibrations which are detrimental to the hydraulic circuit components, the whole machine and the operator.

Attempts to cure the problem have employed hydraulic damping, changing of the working pressures and predetermined pressures but have failed. Also attempts to remove hysteresis energy by venting through a throttle have the twin adverse effects of power loss and undue oil temperature rise.

The object of the present invention is to obviate or mitigate the above disadvantages.

According to the present invention there is provided a hydraulic control system comprising a reservoir for hydraulic fluid, a main pump, a fluid pressure actuator and a control valve for control of pressure fluid therebetween, an auxiliary pump and an auxiliary valve means adapted to channel pressure fluid from said auxiliary puinp alternatively into said circuit or to the reservoir, control means for conditioning said auxiliary valve means in response to the presence or absence of a pressure level of predetermined value in said actuator wherein said control means incorporates a time delay device which is operative to delay the change in condition of said auxiliary valve means when the pressure level reaches said predetermined value.

The invention will now be described with reference to the accompanying drawings of which:

FIG. 1 is a side elevation of a typical machine to which the present invention would be applicable.

FIG. 2 is a plan view of the machine of FIG. 1 and illustrates the disposition of the hydraulic cylinders that are involved.

FIG. 3 is a diagrammatic illustration ofa first hydraulic circuit.

FIGS. 4 and 5 are diagrammatic native hydraulic circuits.

FIGS. 1 and 2 show an articulated wheeled loader 30 having two pairs of driving wheels 31 supporting the illustrations of alterfront body 32 and the rear body 33. The two bodies are joined together at the pivot 34. The front body 32 carries a drivers cab 35, a pair of lift arms 36, a bucket 37 pivotted on the end of the lift arms 36, a bucket tilt linkage 38 mounted on the lift arms and connected to the bucket 37, hydraulic bucket cylinders 9 for moving the tilt linkage 38 and bucket 37, and hydraulic lift cylinders 10 for raising and lowering the lift arms.

The rear body 33 supports the engine and transmission assembly which is hidden beneath the hood 41. The engine also drives the hydraulic pumps. The front and rear bodies are pivotable with respect to each other to effect steering by means of a pair of steering cylinders 42 disposed on opposite sides of pivot 34.

In use the bucket is loaded by driving it into a pile of material, tilting the bucket back by extending bucket cylinder 9 followed by reversing out of the pile. Simultaneously with reversing or other movement of the loader 30 the cylinders 10 are used to raise the load to a sufficient height for dumping e.g. into a truck. If the bucket is carrying its maximum load the bouncing movement along uneven terrain may cause high pressure peaks in the hydraulic circuit. These pressure peaks cause the undesirable vibration and oil heating effects which have been previously referred to and which are now mitigated by the present invention. This condition can be met if an unusually high load is applied suddenly to the bucket e.g. if a large rock falls on to the bucket whilst the loader is working at the rockface.

In FIGS. 3, 4 and 5 the symbols used are in accordance with International Standards Office Publication No. R 2917. All controls are shown in their inactive positions.

The arrangement shown in FIG. 3 comprises an engine-driven hydraulic pump P1 which draws hydraulic flud from tank 19 via line 1 and delivers it via lines 2 and 3 to a control unit 4. Control spool-valve 4a is contained within the unit 4 and this is adapted to supply pressure fluid to one of lines 5 and 5a. Control spool valve 4b serves a similar purpose for lines 6 and 6a. Lines 5 and 5a serve a hydraulic actuator 9 and lines 6 and 6a serve actuator 10. The actuator 9 is the bucket cylinder and the actuator 10 is the boom lift cylinder of the machine shown in FIGS. 1 and 2. The control unit 4 also includes a pressure relief valve 41: which is adapted to protect the circuit.

An engine driven standby pump P2 is also provided. This delivers into a pressure line 17 and through a nonreturn valve 15 into line 3. Pressure line 17 and return line 18 are connected together by a normally open pressure control valve 14. This valve 14 is a pilot operated valve which is spring loaded to the open position and on receipt of a pressure signal it closes. The signal is provided by means of a three port two position valve 16 which is connected to pressure line 3, to return line 18, and to valve 14 and is spring loaded in a direction such that in its normal condition zero pressure is applied to valve 14. A solenoid 16a is employed to alter the valve 16 against the spring so that pressure from line 3 is applied to valve 14.

Pressure in cylinder 10 is constantly applied to a valve actuator 11a which, at a predermined pressure level, is adapted to close an electrical switch 11. The pressure level at which the electrical switch 11 closes is pre-set at the factory. The switch 11 is in an electrical circuit 12 which begins at the electric battery 50 and includes in series a time delay device 13a and a solenoid 13c which operates on being energized to open an electric switch 13d. A second electrical circuit 13b includes in series the switch 13d and solenoid 16a. A master switch 51 which is closed when the engine is started also makes the circuit 13b live and energizes solenoid 16a to change valve 16 so that pressure from line 3 is adapted to close control valve 14.

The open centre spool valve 4a is manually operated and spring centred and is in series flow connection with a similar valve 4b.

In operation let it be assumed that the bucket has been filled and is being lifted by cylinder 10. The pressure in cylinder is applied to the pressure control valve 14 via valve 16 and accordingly valve 14 is in a condition where it prevents flow from pump P2 passing to the tank and causes the flow to pass into pressure line 3.

When the pressure rises to a level where it closes switch 11, the time delay device 13a operates and after an appropriate length of time the circuit 12 which includes solenoid 130 is completed causing the latter to open switch 13d. This breaks the second electrical circuit 13b and de-energizes solenoid 16a. The valve 16 changes to divert the flow from pump P2 to tank through valve 14. Discharge of pressure fluid from line 3 is prevented by check valve 15.

The delay introduced by the device 13 prevents transient pressure surges from cutting flow from pump P2 out of the implement hydraulic circuit and consequently the occurrence of harmful vibrations.

in the arrangement according to FIG. 4 the second electrical circuit 13b which includes solenoid 16a incorporates two further switches and 21. Switchs 20, 21 are operated by spool valves 4a and 41; respectively in either direction away from their mid-positions. The two switches 20 and 21 are in parallel.

Also in FIG. 4 the illustrated position of valve 16 permits valve 14 to remain in its normally open position and solenoid 16a has to be energized to enable pressure from line 3 to close valve 14.

The operation is such that if either of switches 20 or 21 is closed the solenoid 16a is energised and the valve 14 is closed causing flowfrom pump P2 to enter line 3. If subsequently switch 11 is closed due to a pressure rise to the pretermined level in cylinder 10 the circuit 13b is broken, solenoid 16a is de-energized the valve 14 opens and flow from pump P2 returns to tank, after the appropriate delay. The flow from pump P2 is returned to tank instantly if switch 20 or 21 is opened by centralizing of valves 4a and 4b and consequently saves energy.

In the arrangement shown in FIG. 5 the main work pump P1 supplies flow for the implement hydraulic circuit, the stand-by pump P2 supplies additional flow thereto and a steering pump P3 supplies the steering hydraulic circuit 17b which includes steering cylinders 42. A steering wheel actuated valve 43 controls the flow to cylinder 42.

The pumps P2 and P3 draw fluid through line 17a. Pump P3 delivers to circuit 17b which contains a throttle 2212. Pressure sensing lines 220 are applied to valve actuators 22d which operate on a flow divider valve 22a. This flow divider valve 22a receives the flow from standby pump P2 through line 170.

In this condition of the valve 22a seen in FIG. 5 the engine will be running relatively slowly and the flow from pump P3 will be relatively low,..The loader will be travelling slowly and a high rate of steering will be required. Accordingly the flow from pump P2 will be diverted to circuit 171; where it will contribute to a high steering rate.

In the condition where the engine is running at high speed the lower actuator 22d will move the valve 22a to its centre position and divert the P2 flow to steering circuit 17b or to valve 14 whichever path offers least resistance.

In the condition where the engine is running at high speed and there is no demand from the steering valve the pressure downstream of throttle 22b will be almost zero and the lower actuator 22d will cause valve 22a to take up the third position where all the flow from P2 is diverted to valve 14 where it may or may not be diverted to assist the flow from P1 depending on the condition of switches 20, 21 and 11 as explained previously with reference to FIG. 4.

We claim:

1. A hydraulic control system comprising a reservoir for hydraulic fluid, a main pump, a fluid pressure actuator and a control valve for control of pressure fluid therebetween, an auxiliary pump and an auxiliary valve means adapted to channel pressure fluid from said auxiliary pump alternatively into said circuit or to the reservoir, control means for conditioning said auxiliary valve means including a conduit for sensing the pressure of said actuator in response to a pressure level of predetermined value in said actuator wherein said control means incorporates a time delay device which is operative in response to the pressure in said conduit to delay the change in condition of said auxiliary valve means when the pressure level reaches said predetermined value.

2. A hydraulic system according to claim 1 wherein at least part of the control means is electrical.

3. A hydraulic system according to claim 2 wherein control means includes i. a first circuit having the time delay device, a pressure sensitive switch responsive to presssure in the fluid pressure actuator and a first electric actuator for a second switch,

ii. a second circuit including said second switch and a second electric actuator and iii. a hydraulic valve movable between first and second positions by said second electric actuator so that presence of a pressure in excess of a predetermined pressure in said fluid pressure actuator causes after a delay said hydraulic valve to move from its first position in which it maintains said auxiliary valve means in a position where auxiliary pump flow enters said circuit, to a second position in which auxiliary pump flow is channelled to the reservoir.

4. A hydraulic system according to claim 3 wherein said second circuit incorporates a further switch in series with said second switch which is operable with said control valve and which on being opened, by movement of the control valve to an inactive position is adapted to cause without delay said hydraulic valve to move from its first position to its second position.

5. A hydraulic control system according to claim 1 wherein said time delay device is operative to delay the conditioning of said auxiliary valve means from a condition where it is channelling pressure fluid into said 7. A hydraulic system according to claim 1 in which the pressure sensitive switch is positioned between the control valve and the main pump.

8. A hydraulic system according to claim 1 in which said presure sensitive switch is positioned between the central valve and one of said actuators. 

1. A hydraulic control system comprising a reservoir for hydraulic fluid, a main pump, a fluid pressure actuator and a control valve for control of pressure fluid therebetween, an auxiliary pump and an auxiliary valve means adapted to channel pressure fluid from said auxiliary pump alternatively into said circuit or to the reservoir, control means for conditioning said auxiliary valve means including a conduit for sensing the pressure of said actuator in response to a pressure level of predetermined value in said actuator wherein said control means incorporates a time delay device which is operative in response to the pressure in said conduit to delay the change in condition of said auxiliary valve means when the pressure level reaches said predetermined value.
 2. A hydraulic system according to claim 1 wherein at least part of the control means is electrical.
 3. A hydraulic system according to claim 2 wherein control means includes i. a first circuit having the time delay device, a pressure sensitive switch responsive to presssure in the fluid pressure actuator and a first electric actuator for a second switch, ii. a second circuit including said second switch and a second electric actuator and iii. a hydraulic valve movable between first and second positions by said second electric actuator so that presence of a pressure in excess of a predetermined pressure in said fluid pressure actuator causes after a delay said hydraulic valve to move from its first position in which it maintains said auxiliary valve means in a position where auxiliary pump flow enters said circuit, to a second position in which auxiliary pump flow is channelled to the reservoir.
 4. A hydraulic system according to claim 3 wherein said second circuit incorporates a further switch in series with said second switch which is operable with said control valve and which on being opened, by movement of the control valve to an inactive position is adapted to cause without delay said hydraulic valve to move from its first position to its second position.
 5. A hydraulic control system according to claim 1 wherein said time delay device is operative to delay the conditioning of said auxiliary valve means from a condition where it is channelling pressure fluid into said circuit to a condition where it is channelling fluid to the reservoir.
 6. A hydraulic system according to claim 1 wherein a further motor driven hydraulic pump is provided for the supply of a steering circuit and a distributor valve which enables the auxiliary pump to be switched to the steering circuit (17b) or to said first circuit or to both said circuits simultaneously.
 7. A hydraulic system according to claim 1 in which the pressure sensitive switch is positioned between the control valve and the main pump.
 8. A hydraulic system according to claim 1 in which said presure sensitive switch is positioned between the central valve and one of said actuators. 